1. Technical Field
The invention disclosed broadly relates to power circuits and methods and more particularly relates to an improved power transfer circuit for maintaining continuity during power transfer operations.
2. Background Art
Switching of power systems from one source of energy to another frequently causes unwanted interruptions to the operation of electronic equipment. The duration of this outage is sufficient to cause loss of volatile data and frequently resets the operation of complex electrical machines. Power switching events often occur in situations such as the transfer from ground to on-board power in present aircraft designs. Power switching is also required by the power utility companies for the rotation of equipment during maintenance or recovery from equipment failures.
The speed of operation of an electro-mechanical contactor is dependent on its construction, temperature, position, and the voltage applied to the coil. It is not advisable for several contactors to be interconnected for the purpose of switching power without allowing sufficient "dead time" between them to eliminate overlap. Variability in relay timing necessitates a time period many milliseconds wide to eliminate overlap during sequential switching of relays. Repeatable power outages as short as a few milliseconds in duration are difficult to achieve with relays and are still too long for sensitive electrical equipment to tolerate. Unsynchronized power systems must never be interconnected as the relative voltage differences would generate very large currents to realign the alternators in an explosive fashion and would probably destroy both machines. There is a severe risk of electrical and mechanical damage if asynchronous power systems are electrically connected together without special precautions.